The invention is concerned with a system of driving by electric motor machines which work in a periodic manner.
Machines having torques variable as a function of the angle of rotation are, e.g., piston driving mechanisms such as compressors or cam driving mechanisms or printing machines and looms. Typical of the behavior of these machines is the torque changing as a function of the angular position of the driving shaft, the trend of the torque repeating periodically and only changing little over succeeding periods. The driving problems with torques variable as a function of the angle of rotation and representative of the machines already mentioned are further shown in the example of looms.
For driving fast running looms by means of an electric motor three operational states are to be distinguished, each of which imposes specific demands. These are the starting behavior, the behavior at shutdown and the behavior while running.
The effects of the torques variable as a function of the angle of rotation make themselves felt predominantly in the behavior while running.
Characteristic of the weaving process are the wide differences in the power needed by the individual mechanisms during one revolution of the main shaft. Through the starting of different sequences such, e.g., as formation of the shed, movement of the reed or warp let-off energy is needed on short notice as a function of the angle of rotation of the main shaft, which makes itself felt in a considerable instantaneous variation in the torque and resulting from that a variation in the angular velocity of the rotating system. Since the individual sequences take place at exactly defined angles of rotation, the torque varies as a function of angle but it varies little from one period or cycle to the next.
The significant variations of the torque as a function of angle cause, for example:
a) vibrations which both internally to the machine and externally, e.g., on the foundations, can act to disturb or even destroy; PA1 b) an influence upon the radiation of noise from noise-generating components such as battens, healds, torsion rods, etc.; PA1 c) alternations in the weaving process which may in certain materials become visible through so-called streakiness; PA1 d) alterations in the tension ratios in the weave which can make themselves felt for the first time in faults in the finish, e.g., the shrinkage behavior.
A driving mechanism would be desirable which enables the kinematic sequences and the torques which occur to be independent of one another. This applies, for example, to a continuous weaving process. The fulfillment of this requirement is particularly difficult during start-up and shutdown of the loom. Here the kinematic desired values should be reached right after switching.
A series of proposals have become known for reaching gradual independence better than is possible with a simple three-phrase drive, including flywheels connected via couplings. These solutions confer advantages in sub-ranges. Flywheels enable a reduction in the variations in torque but not any active influence or any elimination at all. Up to now there has been no success, within a justifiable economic frame of expenditure, in attempts to uncouple kinematics and torque for periodically working machines with the torque variable as a function of the angle of rotation, such as, for example, loom drives. The application of a classical regulator and regulation, e.g., to assure a constant angular velocity relies on the presence of an error in the regulating process, or a deviation in regulation, whereby the desired independence between the two does not exist.